If you’ve only got access to an iOS device, that’s true I guess.
But if you happen to have DT as well, you can use mail rules in macOS to automatically import mails into DT and as a bonus you can simultaneously add a hyperlink to the corresponding email in Mail with this script @BLUEFROG kindly created:
The beauty of that script is that the links to those e-mails also work in iOS or iPadOS Mail as long as you setup the same mail account you use on macOS on those iOS devices.
So when I now receive an e-mail, it is automatically imported into DT, and when I want to reply to that mail I can simply click the hyperlink to open that specific email on any device using either iOS Mail or macOS Mail.